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[email protected]System-10-MOD Network Interface Installation Guide 05/14 - 0653-10 / 18321 Page 19
SECTION 2.0: MODBUS MEMORY MAP
ONICON Btu meters equipped with MODBUS serial communications provide energy and volume rate
data, and totalized energy and volume data in a variety of engineering units. You select the engineering
units you wish to use by mapping to the appropriate registers.
Also supplied with your System-10 is a document titled “Recommended MODBUS Conguration
Data”. This document is different for each Btu meter. It provides a suggested list of registers to use. The
recommendations are based on the calibration of the ow meter and the programming of units and
multipliers displayed on the System-10.
2.1 MODBUS REGISTER FORMAT AND NETWORKING INFORMATION
1. All registers are 16 bit MODBUS Holding Registers.
2. MODBUS Holding Registers are used in 4 different ways.
A. As an Analog Value: In some cases these values are scaled
by multiplying the register contents by a xed multiplier.
B. As a status indicator where the register value can only
be “1” or “2”.
C. As a mode indicator where the value indicates current operating mode
such as “1” = single, “2” = dual, or “3” = bi-directional.
D. As a control register where the host can write a value to reset total(s).
3. Registers 40001 through 40068 are unsigned integer registers (0 to 65,535) except for 40024
and 40025. These are 16 bit signed integer values (-32,768 to +32,767). Registers 41003
through 41081 are 32 bit single precision oating point values. 41001, 41002 and 41065
through 41069 are unsigned integer registers.
4. System-10 MODBUS register addresses are formatted as follows:
Example: address 40001
4 = Holding register
0001 = Address that corresponds to memory location 0000
5. MODBUS function codes supported:
CODE DESCRIPTION
03 Read Holding Registers
06 Preset Single Registers
16 Preset Multiple Registers
17 Report Slave ID
IMPORTANT NOTE
ONICON provides data in integer and oating point format. We recommend the use of oating
point registers to transmit data to the network. The use of oating point data eliminates the need
for scaling and additional mathematical operations to totalize energy and ow.
(32 pages)
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